The Dark and Hollow Places (Forest of Hands and Teeth Trilogy);

There are many things that Annah would like to forget: the look on her sister's face before Annah left her behind in the Forest of Hands and Teeth, her first glimpse of the Horde as they swarmed the Dark City, the sear of the barbed wire that would scar her for life. But most of all, Annah would like to forget the morning Elias left her for the Recruiters.  
Annah's world stopped that day, and she's been waiting for Elias to come home ever since. Somehow, without him, her life doesn't feel much different than the dead that roam the wasted city around her. Until she meets Catcher, and everything feels alive again.
But Catcher has his own secrets. Dark, terrifying truths that link him to a past Annah has longed to forget, and to a future too deadly to consider. And now it's up to Annah: can she continue to live in a world covered in the blood of the living? Or is death the only escape from the Return's destruction?